The present invention is related to a hydrolyzed ethylene-vinyl acetate copolymer composition, and more particularly to a hydrolyzed ethylene-vinyl acetate copolymer composition having excellent adhesive strength to a polyolefin modified with an unsaturated carboxylic acid which are widely used as a tie resin layer upon lamination of a polyolefin layer and a hydrolyzed ethylene-vinyl acetate copolymer layer.
Two or more-layer laminates having a structure wherein polyolefin layers and hydrolyzed ethylene-vinyl acetate copolymer layers are laminated are well-balanced in excellent water resistance resulting from the polyolefin and in excellent oxygen impermeability, oil resistance and solvent resistance resulting from the hydrolyzed ethylene-vinyl acetate copolymer. So, the laminates of the polyolefin layers and the hydrolyzed ethylene-vinyl acetate copolymer layers are expected to be used for various uses including wrapping and packaging materials such as films, sheets, bags or containers for foods. The polyolefins and the hydrolyzed ethylene-vinyl acetate copolymer, however, adhere unsatisfactorily to each other. Therefore, even if these two kinds of the resins are laminated by means of a melt coextrusion or a melt coating, the obtained laminates cause interlayer peeling between the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer, which are not practically used.
In order to improve the interlayer peeling in the laminate of the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer, it has been proposed (1) to blend at least one of the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer with the resin composing of the other layer, (2) to blend at least one of the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer with a resin capable of imparting adhesive strength such as ethylene-acrylic acid ester copolymer, an ionomer, a hydrolyzed ethylene-vinyl acetate copolymer rich in an ethylene content or a polyolefin grafted with an unsaturated polyvalent carboxylic acid, and the like. However, when blending the above-mentioned other resin with the hydrolyzed ethylene-vinyl acetate copolymer, it tends to impair the excellent oxygen impermeability and oil or solvent resistance originally existing in the hydrolyzed copolymer. On the other hand, when blending the other resin with the polyolefin, it tends to impair the excellent transparency and surface smoothness. The improvement of adhesive strength is unsatisfactory in the both cases.
In order to improve the adhesive strength between the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer solving the above-mentioned defects, it has been tried to study in various ways as to methods in which a tie resin layer is laid between the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer. Japanese Unexamined Patent Publication No. 112887/1976 discloses polyolefins modified with unsaturated carboxylic acids as the tie resin. In the above methods, since both the polyolefin layer and the hydrolyzed ethylene-vinyl acetate copolymer layer do not blend with the other resins, the excellent properties originally existing in the polyolefin and the hydrolyzed ethylene-vinyl acetate copolymer remain intact, but the obtained laminates are practically unsatisfactory in the adhesive strength between the hydrolyzed ethylene-vinyl acetate copolymer and the tie resin.
An object of the invention is to provide a hydrolyzed ethylene-vinyl acetate copolymer composition having excellent adhesive strength to a tie resin of a polyolefin modified with an unsaturated carboxylic acid.
This and other objects of the present invention will become apparent from the following description.